A method in the prior-art for forming diamond and diamondlike films is by chemical vapor deposition (CVD). Generally in this method, a gas stream containing a carbon-containing gas and hydrogen is passed over a heating element, such as a hot filament, which decomposes the carbon-containing gas. The heated gas stream is passed over a substrate heated to a temperature lower than the heating element, and carbon from the gas is deposited upon a substrate. Depending upon the composition of the gas stream and the process conditions, a diamond film or a diamondlike film may be formed on the substrate. A diamond film is a film consisting essentially of carbon in a diamond phase with fourfold coordination (sp.sup.3). A diamondlike carbon (DLC) film is a film with mixed carbon phases, mostly diamond phase mixed with a three fold coordination graphite phase (sp.sup.2), as well as polymeric carbon phases. Because of their unique properties, i.e., optical transparency over a wide spectral range, good electrical insulation, chemical inertness and extreme hardness, diamond and DLC films have attracted considerable interest. Possible applications for these films include anti-reflection coatings for infrared optics and silicon solar cells, and coatings to reduce wear and corrosion.
An example of a CVD process for forming diamond and DLC films is disclosed in U.S. Pat. No. 5,075,094 to Morrish et al. In this process hydrogen and methane at 45 torr were passed over a the heating element is a filament or an arc at a temperature above 1600.degree. C. After heating the gas, the gas was passed over a substrate that was heated to a temperature between 500.degree. C. and 1300.degree. C. The improvement of the Morrish et al. process involved treating the surface of the substrate with oil before the CVD process.
A problem with CVD processes is that they require expensive equipment, e.g. vacuum chambers, gas flow control systems, high temperature heating systems and controls. In addition, the process requires that the substrate be heated, which precludes the use of substrates which decompose or are altered by heating in the CVD process. For example, many tempered or hardened steel alloys will loose their temper at substrate temperatures in CVD processes.
Diamond films have been formed by immersing a substrate in a fluid medium comprising a carbon-containing precursor and irradiating the substrate with a laser to pyrolyze the precursor. For example, in U.S. Pat. No. 4,948,629 to Hacker et al. is disclosed a process for the deposition of diamond films where gas containing an aliphatic acid or an aromatic carboxylic anhydride that vaporizes without decomposition is passed over a substrate and irradiated with a focused high-powered, pulsed laser. Also in U.S. Pat. No. 4,954,365 to Neifeld is disclosed a process where the substrate is immersed in a liquid containing carbon and hydrogen, e.g. methanol. A laser pulse is then directed through the liquid coating to heat the substrate. The liquid is pyrolyzed and carbon material from the pyrolyzed liquid grows on the substrate to form a diamond coating on the substrate.
Other examples of the use of a laser to form a diamond films is disclosed in Japanese Patent 63-093,867 (as disclosed in Derwent Abstract 88-152150/22), which describes formation of amorphous diamond thin films by irradiating a non-converging laser beam onto a substrate.
It is also known to coat a precursor upon a substrate and pyrolize the precursor to form a final film. For example, in U.S. Pat. No. 4,916,115 to Mantese et al. a process is disclosed for forming patterned thin film superconductors. The process comprises coating a substrate with solution of a metal oxide precursor and a light absorbing dye. A focused laser light is then scanned across the surface to locally pyrolyze the precursor to the metal oxide.
Layers of molecules applied on a substrate by the Langmuir-Blodgett technique are known in the art for numerous applications, such as disclosed in U.S. Pat. Nos. 5,093,154 to Hatada et al., and 4,996,075 to Ogawa et al. Treatment of LB layers to more firmly adhere the layer to the substrate or modify the surface of the LB layer is known. The teaching of the prior-art is to preserve the essential chemical character of the film, and the prior-art methods are directed at modifying or enhancing the film properties. However, pyrolyzing a LB layer as a precursor to a completely reformed film, as in the present invention is not known.